Numerical Analysis of Thermal Multilayer Insulations with carbon nanofiber spacers

Multilayer insulation using nanofiber materials has been numerically investigated. High surface to volume ratio of nanofibers results an important effect on both the radiation heat transfer and conduction heat transfer. Thus it is considered as an effective spacer of the multilayer insulators for investigation. The radiation heat transfer is calculated considering the optically thick assumption on the fibers and using the diffusion approximation. Thermal conductivity of alumina fiber and carbon nanofiber are determined using experimental results available in the literature. It is presented that the specific extinction coefficient of carbon nanofiber is approximately 31 percent higher than the one of alumina fiber at 500 K. The results show that using carbon nanofiber as the spacer of multilayer insulation improves the insulation performance. Thus it is suggested to be used as the spacer material.